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 |  موضوع: مجموعة أسئلة وأجوبتها عن السباكة الثلاثاء 21 مايو 2013, 9:45 pm | |
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تذكير بمساهمة فاتح الموضوع : أخوانى فى الله
أحضرت لكم كتاب
مجموعة أسئلة و أجوبة فى السباكة
Casting Questions and Answers
QUESTIONS
Q1 : Give the stages through which the metal flows in a foundry.
-1تسخين المعدن
-2صب المصهور في قالب له شكل و أبعاد المنتج المطلوب
-3ترك المصهور حتى يتجمد
-4اخراج المسبوك من القالب
-5التأكد من سلامة المسبوك
Q2 : Explain with Examples in what circumstances casting will prove to be the most
economical manufacturing process.
*The Most economical choise of any process will depend on :
1- The Alloy to be cast
2- The size and complexitry of the casting
3- The required quantity
4- Tolerance specified and the surface finish
*The important material factor in fluancing the choise of casting process is the "Melting
Tempreture"
Q3 : Enumerate the Main advantages of the casting processes over other methods of
fabrication.
1- Casting processes are extremely flexible with regard to size and weight. From gram
to 1000 gram in normal production.
2- The ability of casting to produce complex 3D shapes in a simple operation.
3- The minimum section thickness the processes can produce.
Q4 : What are the basic requirements of a pattern material ?
يصنع النموذج من مواد معدنية أو خشبية أو بلاستيكية أو من الشمع بحيث يجب ان تتوافر فيه
الخواص التالية :
-1اندماج البنية
-2قلة الاعوجاج
-3سهولة التشكيل
-4النماذج الخشبية تصلح لانتاج اعداد قليلة مقارنة بالنماذج المعدنية .
Q5 : state the different types of material which are normally used for pattern making.
?الاخشاب :
تصنع النماذج من الاخشاب البيضاء اذا كان عدد المسبوكات قليل و تصنع من اخشاب
(الماهونجي-الباس-الصنوبر-الخشب الاحمر)
?المعادن :
نلجأ الى استخدام المعادن اذا كان المطلوب اعداد كبيرة من المسبوكات او عمر طويل
للنموذج. من أشهر المواد المستخدمة هو الألومنيوم ثم النحاس ثم البرونز.. و السبائك
ذات درجات الانصهار المنخفضة .
?البلاستيك :يستخدم هذا النوع في انتاج الاسطح الناعمة"زجاجية" للمسبوكات و هذا
النوع صلب مقاوم للتاكل .
?الشمع .
Q6 : Discuss, with help of any suitable examples, the various types of allowances which
should be provided to a pattern made of cast iron and state their amounts.
-1سماح الانكماش :
هو مقدار الزيادة في الحجم والتى تضاف على النموذج لتعويض قيمة الانكماش الذي
سيحدث للمنصهر عندما يبدأ في عملية التبريد و يتم ذلك باستخدام مسطرة
الانكماش الخاصة بالمادة المسبوكة .. حيث انه تتراوح نسبة الانكماش في الحديد
الزهر ( % ) 2.4 : 1
-2سماح التشغيل :
هو مقدار الزيادة في الابعاد التى تضاف للنموذج وذلك لتعويض ما سيتم ازالته اثناء
عمليات التشطيب اللاحقة وتعتمد هذه الزيادة على أسلوب السباكة و درجة
التشطيب المرغوبة .
-3سماح السلبة :
هو مقدار الميل الذي تأخذه الاسطح الرأسية و ذلك لتسهيل سحب النموذج من
القالب دون ان تتأثر جدران القالب و يتوقف هذا الميل على شكل و حجم النموذج
ومادة صنعة , ومادة صنع القالب, وطريقة سحب النموذج ( يدوي او ميكانيكي ) .
-4التفاوت الحجمي :
هو مقدار التفاوت المسموح به في أبعاد المسبوك و يساوي نصف سماح الانكماش .
-5سماح الارتجاج :
يؤخذ في الاعتبار في النماذج التي تخرج من القالب بطريقة الطرق,لأن الطرق يؤدي الى
زيادة أبعاد القالب و بالتالي يصنع النوذج أقل من حجم المنتج .
Q7 : Critically analysis the various pattern allowances. What is their influence on the
production of accurate castings?
Q8 : What are the basic pattern design criteria. Discuss them with Examples.
-1يصنع النموذج بحيث يناسب القالب المستخدم .
chills - Risers – Gates : - يجب تحديد اماكن كلا من2
-3اخذ الحجم والشكل في الاعتبار منعا لتكون الشرخ .
-4لابد من تحقيق عملية التجمد الاتجاهى للمسبوك .
Q9 : Describe the various types of core boxe. What are the usually allowances given on
them.
1- Half core Box
When the shape of the core is such that it can be produced in identical halves , a half
core box is used.
2- Split core Box
The core box is in two halves with a split.
3- Dump or Slab core Box
If the shape of core is simple enough so that it can be prepared in one piece form an
open core box.Q10 : Describe any widely accepted color code for identifying the different parts of the
pattern and core box.
Q11 : What are the basic requirements of a proper molding sand?
1- Strength ;
a- Green Strength ;
باضافة الماء على الرمل يجب ان يظل الرمل محتفظا بالجساءة و المتانة اللازمة
للحفاظ على شكل القالب المتكون منه للحصول على منتج جيد ذو درجة تشطيب
عالية
b- Dry Strength ;
عند صب المصهور داخل القالب تفقد الجدران الداخلية للقالب الرطوبة الموجودة بها و
تتحول الى الصورة الجافة. و لذلك يجب ان يكون الرمل في هذه الحالة قادر على تحمل
الضغط العالي للمصهور .
c- Hot strength ;
- the dry sand must have strength at very high temprture.
2- Permiability of Porosity :
The molding sand has porosity between its particles which help in removing the
vapor and gases through the walls of mold.
3- Thermal Stability ;
أثناء عملية التسخين السريع تحدث عملية تمدد لجدران الرمال الداخلي مما تؤدي
الى تولد شروخ.
4- Refractoriness ;
(Pure Silica+potach+lime) --? silicat
5- Core Coatings.
6- Collapsibillity
7- Flowability
8- Chemical Resulting
9- Plasticity
Q12: Explain how green strength and permeability are affected by:
? Grain shape of the sand
? The grain shape could be round or regular
? The round grains have lower permeability compered to angular grains.
? The strength of round grains less than the strength if angular grains.
? Grain size of the sand
? The grain size could be fine or coarse
? The coarse grain have great permeability, low strength.
? The fine grains have low permeability, high strength.
? Grain size distribution
If the sand is found in various sizes, the strength increase and permeability decrease.
Q13: Distinguish between pore water and free water. Explain their effects on the Green
strength of the sand.
Wrong control in water percentage may produce:
1- Under develop green strength
2- Pour scratch hardness3- Edge hardness
4- Low baked tensile strength
5- Excessive water :
? Stratification of binders by leakage
? Stickness and surface crusting
Q14: Name the Various additives used in molding sand and explain how they affect its
properties.
Special Additives:
1- Core oil : 0.5 : 3 % (( used as binder ))
2- Soluble binder ? 0.5: 2 % used for green strength
*To Avoid reduction in hardness and strength.
3- Pitch; It's made from coke, it has a percentage up to 3%.
Q15: Describe briefly, with help of sketch, how you would test the permeability of molding
sand. What do you understand by permeability number?
The rate of flow air passing through as tanderd specimen under a standard pressure.
*The standard permeability test: Is to measure the time taken by 2000 cm? of air with a
pressure of 980 pa.
To pass through a standard specimen.
The Standard specimen size is 50mm in dia. And Length of 50.8mm
The permeability number can be obtained:
P = V H ÷ P A T
*note; the permeability test for 2 sands
1- Green sand
2- Dry Sand
Q16: Define the specific surface area of sand grains. Given a suitable method to
determine the same.
Q17: Given the importance of mulling and explain how it affect the properties of the
mold sand.
Q18: Discus the various types of cores given their specific uses.
*There are many types of cores, the most common types are:
(a) Horizontal core: This core is usually in a cylindrical form and is laid horizontally in
the mold. The ends of the core rest in the seats provided by the core prints on the
pattern.
(b) Vertical core: The ends of the core at the top and the bottom fit into seats
provided in the cope and drag halves if the mold.Q19 : What are the basic requirements of a core sand ? In What respect does it
differ from the molding sand?
1- Coars must have sufficient hardness as well as strength in both dry and green
sand
2- Cores must be permeable to to allow gases to be escaped easly.
3- Must with sand the high temperature of the molten metal
4- It should be collapsible
Q20 : Differentiate between the following :
(a) Pit molding & Floor molding
? Pit molding :
الصب يكون في قوالب صغيرة و تصلح لانتاج المسبوكات الصغيرة الى حد ما
? Floor molding :
الصب في حيز بأرضية المسبك وهي تصلح للمصبوبات المعقدة و الكبيرة الحجم
(b) Green Sand molding and dry sand molding
? Green sand :
Sand is green or most condition. Its common practice for most of small and
medium sized ferrous and non-ferrous casting.
? Dry sand :
Moisture is removed by heating in a dry over. Its mainly used for the
production of larger casting, dimensional accuracy is needed.
Q21 : What are the main operations performed by the molding machines and show,
with sketches, how the are done !
The Molding Machines in general use produce compaction by repeated jolting or by
combination of jolting and squeezing , the former produces a less uniform and less
dense mold than the latter. Jolt squeeze machines are necessary for making large
molds and when high rates of production are required .
Q22: What are the various steps in shell molding? Given the main advantages of
shell molding over molding processes.
SHEL MOLDING
هذه الطريقة تتم من خلال وضع الكل المراد عمله داخل فرن يتم رشه باستخدام ?
الرمال, التي تكون مصهورة بمواد رابطة,فتترسب على الشكل مكونتا الاسطمبة .
تستخدم هذه الطريقة في انتاج اواني الطهي "البيركس".
المميزات :
-1سطح القالب الداخلي يكون ناعم لدرجة عالية مما يسهل من عملية الصب وتجعل
المتنج جيد التشطيب مما يؤدي الى تقليل العمليات الاضافية فتقل التكلفة .
-2معظم المعادن التي تنتج بالسباكة الرملية يمكن ان تنتج بهذه الطريقة .
-3تستخدم في الانتاج الكمي
-4يمكن انتاج الاشكال المعقدة
-5لا تحتاج الى عدد كبير من العمالةQ23: What shell molding is adaptable to a high degree of mechanization?
? Production of shell mold using lower-type dump box must deal with the
following properties :
(a) Good surface finish
(b) Good detail definition
(c) Used for medium size production
Q24: What are the main advantages of permanent mold over sand molds ?
? The parts of mold the cope and the drag are made from "Metal"
? The Process is suitable For :
(a) High volume production of small and simple casting without complex
undercut or intericat
(b)Good surface finish can be obtained
Q25: Critically discuss various factors affecting the rate of solidification in a metallic
mold?
Q26: Discuss the use of chills, chapter, exothermic materials and riser in making
casting. Illustrate with suitable examples.
? Chills :
Provide in the mold to increase the heat extraction capability of the
sand mold. It provides steeper temperature gradient so that the
directional solidification as required in a casting to optained. The chills
are metallic objects having higher heat absorbing capability than the
sand mold. It have two types :
(a) External chills
(b) Internal chills
? Chapter :
? Exothermic :
It uses in riser to reduce the piping tendency and decrease amount of
metal required in riser.
? Risers :
Is used to feed a metal to the cast as it solidifies it may also be
considered as a part of gating system. The riser requirement depends
considerably on the type of metal being poured.
Q27:what are the various methods employed to trap dross and dirt in the gating of
castings ?
? Enlargement :
Enlargement in the feeding system to reduce the velocity of flow, or
special devices such as whir/gate, which whirls the dross and slag in
to the center of riser.
? In Aluminum casting it has been recommended that runner be
placed in mold cavity.
? For Ferrous metal, The reverse situation has been suggested with
the runner in the cope and the in gate in the drag.Q28: Discuss the influence of the following in cupola melting :
(a) Coke-bed height
The heat for the process is supplied by a bed of coke, on the top of which are
placed alternative layers of iron, coke and limestone. Air from a blower
ascend through the upper charge of metal. As the coke in the bed is
consumed, the heat released melts the metal. Then the fresh coke between
the charges reaches the bed and the process continuous.
(b) Iron-coke ratio
The melting rate in turn maybe determined the ratio of coke to iron after the
bed is formed.
This ratio is expressed as a hole number denoting the pounds of iron melted
per pound of coke used.
(c) Air flow rate
The rate of melting increased by increasing the rate of flow of air or
increasing the air temperature by blast preheating.
P=64?g. fc
Q29: Discuss the importance of the following furnaces in the steel melting practice :
(a) L-D process (b) Kaldo process (c) Rotor process
Q30: Enumerate and compare the various methods for cleaning the casting surfaces.
Q31: Describe a process for producing malleable-iron casting; given the temperature
and time required for annealing.
Q32: Differentiate between the following:
(a) Blow holes and pin holes
(b) Cold shuts and misruns
(c) Rate tail and buckle
(a)Blow holes and pin holes;
? Blow holes : caused by evaporations of gasses during solidification of the
casting
?
(b) Cold shuts and misruns ;
? Misruns : it’s the uncompleted casting caused by the failure of the metal
to fill the mold cavity.
? Cold shuts : it’s a casting where a discontinuity exists due to imperfect
metal convergence, it has appearance of crack or a seam with smooth
rounded edge.
Q33: What to you understand by expansion defects and explain how they occur.
اثتاء عمليه التسخين السريع للمسبوك يؤدي ذلك الي تمدد الجدار الداخلي للرمال مما يؤدي
تولد الشروخ
So the sand used must has thermal stability.Q34: Describe X-ray and gamma ray techniques of non-destructive testing.
موجات ذات طول موجي قصير يمكن لها اختراق الاجسام و يمكن استقبالها على افلام خاصة
حيث تظهر المناطق ذات العيوب على الفيلم مناطق اشد سواد من المناطق الاخرى الخالية
من العيوب .
Q35: Discuss the merits and demerits of radio graphic inspection.
The disadvantage to using film is that it takes time. Sometimes, companies prefer to use
real time inspection, in which the radiographic image is displayed on a monitor as a
device is moved over the object being inspected. This method tends to have less clear
resolution, and it doesn't create a permanent record like film does unless the real
time inspection is recorded, as is done in some cases. The advantage is that it can be
done very quickly, which can be key during rapid inspection and repair.
Q36: What metals are commonly cast by die casting process? What are the
advantages and limitations of this process over their processes?
zinc, copper, aluminium,magnesium, lead, pewter and tin based alloys. Depending on the
type of metal being cast, a hot- or cold-chamber machine is used.
? Advantages:
? Excellent dimensional accuracy (dependent on casting material, but typically 0.1 mm for
the first 2.5 cm (0.005 inch for the first inch) and 0.02 mm for each additional centimeter
(0.002 inch for each additional inch).
? Smooth cast surfaces (Ra 1–2.5 micrometres or 0.04–0.10 thou rms).
? Thinner walls can be cast as compared to sand and permanent mold casting
(approximately 0.75 mm or 0.030 in).
? Inserts can be cast-in (such as threaded inserts, heating elements, and high strength
bearing surfaces).
? Reduces or eliminates secondary machining operations.
? Rapid production rates.
? Casting tensile strength as high as 415 megapascals (60 ksi).
? Casting of low fluidity metals.
Disadvantage: The main disadvantage to die casting is the very high capital cost
Q37: Describe with help of sketches the various types of die casting machines. State
their advantages and limitations.
1) Hot chamber die casting :
"Used for lower melting point metals"
Such as; Zinc-based alloy
2) Cold Chamber die casting
"Used for higher melting points"
Such as; Aluminum based alloys injected above 500 C.
? The advantage :
It can be maintained during solidification to produce high density casting
of high pressision.? The Limitations :
This process need more grade production requirements and more
intricate sectional requirements tilt the balance in favor of the coldchamber process.
Q38: What casting process will you prefer for the following:
(a) Small zinc casting:
"Die casting"
(b) Small brass gears:
"permanent mold casting"
(c) Aluminum pistons:
"permanent mold casting"
(d) Turbine blades:
"Investement casting"
(e) Cast Iron pipes:
"centrifugal casting"
Q39: Why investment casting process is so versatile as to shapes and produces
excellent dimensional control?
* يتم عمل قالب من الشمع او البلاستيك على حسب المنتج المراد انتاجة
*يتم صب المعدن المستخدم في صنع المنتج
*يتم تركة حتى يتجمد داخل قالب الشمع او البلاستيك
*يتم حرق القالب باستخدام المفاعل فينصهر الشمع او البلاستيك و يتبق المنتج المطلوب .
*يلاحظ انة يتم طلاء السطح الداخلي لقالب الشمع بمادة polystyreneللحصول على سطح
ناعم وذو درجة تشطيب عالية .
Q40: What do you understand by continuous casting? Give its few applications.
*تستخدم هذه الطريقة في حالة المنتجات المتتابعة حيث تكون المادة في الحالة السائلة
تسير على مسارات حتى تصل الى عناصر الدورات والتى تقل من السمك للمادة
*السباكة المستمرة نوعين :
أ- أفقية ب-رأسية
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